2014年南京两次弱降雪过程的对比分析

利用常规观测资料和NCEP再分析资料,结合多普勒雷达等资料,对2014年2月9—10日江苏大部分地区出现的两次弱降雪过程进行了成因分析。结果表明:9日的降雪是由中层西风槽东移影响,槽前西南暖湿气流在低层冷空气垫上爬升所致,是一次层状云降雪;10日的降雪则是低空冷空气主体偏北东移,内陆偏西地区低空风速随之明显减小,而东部沿海地区风速变化不大,从而使得辐合上升区西扩所致;10日低空上升运动带来的低云降雪,尺度小,且具有类似弱对流系统的特征。常规业务中使用的数值预报产品(如EC)并不能准确预报这两次弱降雪过程,特别是10日过程预报效果较差,而WRF模式则对10日过程把握较好。

Comparison analysis on two weak snowfall processes in Nanjing of 2014

By using conventional observation data, NCEP reanalysis data and Doppler radar data, the causes of two weak snowfall events covering most of Jiangsu province during Feb.9-10, 2014 were analyzed. The results suggest that the snowfall event on Feb.9 was mainly caused by the eastward movement of westerly trough in the mid-troposphere and the lifting of the southwest warm and moist air ahead of the trough over a cold air "cushion" in the lower layer, which consequently led to a stratiform snowfall event. However, the snowfall on Feb.10 was primarily due to the northeastward movement of the main body of the low-level cold air, the obvious decreasing of low-level wind speed over the western inland area, little change of wind speed along the eastern coastal area and the westward expansion of the convergence zone. The low clouds snowfall caused by the low-level upward motion within the convergence zone limited to a small horizontal scale, like the weak convective system. The numerical prediction products conventionally used in the operational analysis, such as EC, do not accurately forecast the two weak snowfall events, especially for the case on Feb.10. However, the snowfall event on Feb.10 is simulated fairly well by the WRF model.